Method and apparatus for automatically venting plastic bags

ABSTRACT

Method and apparatus for automatically closing plastic film bags while simultaneously venting the bag in a manner so that the bag is essentially &#39;&#39;&#39;&#39;leak proof,&#39;&#39;&#39;&#39; but yet is able to breathe to avoid expansion of &#39;&#39;&#39;&#39;pillowing&#39;&#39;&#39;&#39; when stored at high temperature. The invention contemplates folding over the top portion of the bag, applying heating along the fold line sufficient to heat plastify the film and while cooperatively shielding short increments of the film; and thereafter squeezing and cooling the film to pressure set the seal. Each shielded increment forms an air vent to the above-noted quality.

United States Patent 1 Armstrong Feb. 13, 1973 METHOD AND APPARATUS FORAUTOMATICALLY VENTING PLASTIC BAGS [75] Inventor: William A. Armstrong,Brookpark,

Ohio

[73] Assignee: Basic Packaging Systems, Inc., Avon Lake, Ohio [22]Filed: Dec. 21, 1970 [21] App1.No.: 99,780

[52] US. Cl. ..53/37, 53/39, 53/46, 53/373, 93/35 R [51] Int. Cl. ..B65b7/08 [58] Field of Search .93/DIG. 1, 8 VB, 8 WA, 35 PC, 93/35 DS, 59MT; 53/37 [56] References Cited UNITED STATES PATENTS 3,516,217 6/1970Gildersleeve .93/35 PC 3/197 l Williams 2,777,491 1/1957 Ashton ..93/35DS 2,798,523 7/1957 Barrett ..93/35 DS 2,660,219 11/1953 Haas ..93/DlG.1 2,720,246 10/1955 Piazze ..93/DIG. 1 3,361,041 1/1968 Grob ..93/8 WAPrimary Examiner-Travis S. McGehee AttorneyGustalo Nunez 5 7 ABSTRACT 2Claims, 7 Drawing Figures PATENTEDFEB 13 ms SHEET 10F 2 QMN w @N 3N wmmg I Q AGE- EQ INVENTOR. WIN/am H. firms/Pony WVN wN aw w M FITTORNEYMETHOD AND APPARATUS FOR AUTOMATICALLY VENTING PLASTIC BAGS BACKGROUNDOF THE INVENTION A continuing problem in employing plastic bags incertain areas of packaging is the inability of the plastic to breathe.Air trapped within plastic bags, for example, tends to expand such thata pillowing or ballooning effect can occur. In severe cases pillowingcan actually cause the bags in a stack to float one on top of the other.This, in turn, effects palletizing operations as the stack is morelikely to topple when handled as a-unit. Moreover, air pressuresdeveloped in the lower bags can reach levels sufficient to cause abursting or rupturing of the bag material with resultant spilling of theproduct contained therewithin.

The aforenoted drawback of plastic bags, that is, the inability of theplastic to breathe, is most usually felt in industrial applicationsusing heavy-duty bags for the packaging of unit lots in the range ofabout to about 100 lbs. Warehouse and freight cars storage temperatures,for example, of as high as 140 F are not unusual, nor is it unusual torequire that such bags be stacked to considerable heights to maximizethe available storage space.

The obvious solution to this problem, of course, is to somehow vent thebag so that the expanded and heated air can escape without damage to thebag. The difficulty, however, is to form a vent of economicalconstruction that permits leakage of air, but yet is sufficiently tightto retain the product even though the same may be finely divided, suchas talc, sugar, salt, fertilizer or the like.

A particularly advantageous vent construction that effectivelyaccomplishes this end is illustrated in US. Pat. No. 3,439,869.Basically that patent discloses that an unusually effective vent can beachieved by folding over the top end of the bag and sealing along thefold line. The patent explicitly discloses the use of non compatiblematerial located in the vicinity of the fold, and which prevents aperfect hermetic seal from forming, thus resulting in a vent. Normallythe vent width will be approximately It; to of an inch. If less thaninch, air passes through the vent only with difficulty, but if muchgreater than of an inch finely divided products can sometimes escape.

The vent, however, requires special fabricating steps to be pre-appliedto the bag material in order to obtain the desired venting action, and,therefore, adds to the eventual price of the bag. Additionally, thesolution or substance of a non-compatible nature that is applied to thebag must be applied only in strategic areas and, therefore, itsapplication is oftentimes less than fully convenient for customarycommercial embodiments.

Accordingly it is among the objects of the present invention to providethe following:

Method and apparatus for automatically venting plastic bags whereinsubstantially no additional cost is required to include the vent in thefinished bag structure.

Such method and apparatus wherein the resultant vent is sufficientlytight to retain even finely divided products, yet readily exhaustsexcess air pressure from within the bag, and which can be convenientlyincorporated into the bag structure either before or after the bag isfilled; and

Such method and apparatus which functions as an integral part of theclosure step following bag filling, and which may be included in presentday packaging lines with only minor modifications being required ofexisting bag closing equipment.

BRIEF SUMMARY OF THE INVENTION Briefly, then, the present inventionresides in a discovery related to bag closure methods and apparatuswherein a vent of high quality can be automatically incorporated intothe bag during closure thereof, and without requirement of complicatedclosure steps; or equipment that would detract from'the convenience andeconomics in providing such a vent structure. Basically the ventcontemplated herein is formed by folding over the top end of the bag,that is, the end where the mouth or fill opening of the bag is located.The plastic along the fold line is then continuously heat plastifiedsuch as by increments which are shielded automatically from the heat.The heat plastified layers are then quickly cooled and squeezed togetherto pressure set the seal. At each of the shielded increments, however,the seal is non-continuous and therefore permits the bag to breathe.Such steps are accomplished automatically by feeding the bag betweenopposed gripping belts past a folding tunnel which automatically foldsover the top portion of the bag. A second set of gripping belts thenreceives the folded-over portion of the bag, and located above thesecond set of belts are radiant heaters which apply heat continuouslyalong the fold line as the bag is moving forward. The second set ofbelts include shields at spaced intervals which cooperate to shieldautomatically discreet portions of the film, thereby automaticallyeffecting the desired vent structure.

DESCRIPTION OF THE DRAWINGS Yet additional objects and advantages of thepresent invention and its numerous and cognate benefits, are even moreapparent and manifest in and by the ensuing description andspecification taken in conjunction with the accompanying drawing, inwhich wheresoever possible, like characters or reference designatecorresponding material and parts throughout the several views thereof inwhich:

FIG. 1 is-a side elevational view schematically illustrating apparatusfor accomplishing the objectives of the present invention;

FIG. 2 is a top view of the apparatus of FIG. 1;

FIGS. 3, 4, and 5 are enlarged cross-sectional views taken alongreference lines 33, 4-4, and 5-5, respectively, of FIG. 1;

FIG. 6 is an enlarged partial side view of certain chain structure usedin the apparatus of FIG. 1, but as viewed separately therefrom; and

FIG. 7 is a view like FIG. 6 only showing the chain structure thereof asviewed from the top.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now more particularlyto the drawings, there is shown in FIGS. 1 and 2, closure sealingapparatus 10 of the general type contemplated for use herein, andcomprising a movable bottom support or conveyor 12. Positionedhorizontally above conveyor 12 is a first set of opposed gripping belts14 and 16.

Belts l4 and 16 can comprise, for example, convenv tional V-beltscomposed of rubber, synthetic rubber, fabric, or like combinations ofthe same, and are movably engaged throughout the length of the innerruns 20 and 22 thereof. The belts are operated at each end aroundpulleys 24 and 26, and 28 and 30, respectively.

Located centrally above belts 14 and 16 is a bag folding station 32comprising a pair of spaced apart guide plates 36 and 38 formed such asof sheet metal of the like. Plates 36 and 38 define therebetween acontinuous gap 40 which is aligned vertically with the interface 42defined between inner runs 20 and 22 (see FIG. 3) A folding tunnel 34 isformed by extending plate 38 upwardly beyond plate 36 starting atapproximately the central part of station 32. Tunnel 34 begins as aslight clockwise directed curl 44. Curl 44 becomes gradually morepronounced and is tapered such that at the midregion of folding tunnel34 and backwardly therefrom, the curl extends in radially spacedrelationship progressively further about plate 36, and with the amountof such radially spacing progressively diminishing toward the end of thefolding tunnel (see FIG. 3).

A second set of gripping belts 46 and 48 is operated horizontally behindfolding station 32 and at a level generally immediately above belts 14and 16.. As may be noted, the forwardmost end of belts 46 and 48 can beoverlapped with belts l4 and 16 to facilitate the transfer of filledbags therebetween, as will be explained in more detail hereinafter.

Belts 46 and 48 can be comprised of fabric or rubber, like belts 14 and16, but preferably embody a connected link construction as illustratedin FIGS. 6 and 7; and therefore are operated at each end around suitablesprocket means 50 and 52, and 54 and 56, respectively.

Referring now more specifically to FIGS. 6 and 7, an exemplary chainconstruction for belts 46 and 48 can include a joined series of metallinks 58, each comprising spaced apart parallel plates 60 and 62rotatably interconnected such as by suitable pin means 64. A pad 66 isaffixed vertically between plates 60 and 62 of each link 58, andcollectively the pads comprise the actual gripping face of each belt.Pads 66 can comprise, for example, a composite structure including afacing 68 of a rubber or synthetic rubber laminated to a rigid backing70 such as of metal or the like.

Additionally, certain paced apart links 58 in each belt 46 and 48include an inverted L-shaped extension 72 affixed to plate 62 thereofadjacent the upper edge of pad 66. Extensions 72 are selectivelypositioned so that pairs of the same, comprising an extension 72 fromeach belt mesh in moving contiguous relationship with each other as thebelts travel along the extent of their inner runs 74 and 76 (See FIG.4). Pairs of extensions 72 thus cooperate to form shields 78 of discreetlength which automatically move at a speed uniform with belts 46 and 48;shields 78 being of a generally inverted U-shaped configuration. Thehollow central region 82 of each shield 78 communicates directly withthe interface 84 defined between belts 46 and 48.

A hollow housing'86 containing elongated resistant heating means or rods88 and 90 is located centrally above belts 46 and 48 at a region spaceddownwardly from folding station 32. The lower-most extent of housing 86defines a continuous opening or gap 92 of sufficient size to receiveshields 78, and which is located centrally between resistant heatingrods 88 and 90. Opening 92 is aligned vertically over and communicateswith interface 84, except at regions where the interface is blocked byshields 78. Contiguous with the opposite edges 94 and 96 definingopening 92 can be positioned suitable water jackets (NOT shown). Thewater jackets can be maintained at a relatively cool temperature bycirculating water therethrough protectively interrupt heat transfer fromresistant heating rods 88 and to belts 46 and 48, and therefore avoidheat damage to the belts.

A third set of horizontal belts 106 and 108 operate at spaced distancebehind belts 46 and 48 approximately longitudinally in line with opening92. The inner runs 110 and 112 of belts 106 and 108 continuously slidebetween a second set of water jackets 114 and 116. Belts 106 and 108comprise, for example, heat conductive material such as thin metalsheeting or the like. Therefore, cooled water or like cooling mediumcirculating in jackets 114 and 116 is able to quickly conduct heat awayfrom the belts to maintain the interface re gion thereof relativelycool. Disposed in the space intermediate the adjacent ends of belts 46and 48, and 106 and 108, are spaced apart stationary vertical guidesections 118 and 120. Sections 118 and 120 gradually converge towardeach other as they approach the latter set of belts 106 and 108.

OPERATION To operate apparatus 10, a bag 122 such as of polyethylene,polypropylene of like packaging film is filled with product 124 andplaced on conveyor 12, and the top end 126 of the bag manually orautomatically fed between the first pair of gripping belts 14 and 16.Belts 14 and 16 assisted by bottom conveyor 12 automatically forward thebag to folding tunnel 34 where the top end 126 thereof is graduallyfolded over plate 38 by sliding contact with curled plate 36. Bag 122thus emerges from tunnel 34 with the film at its top end 126 snuglyfolded or doubled over, thereby closing the fill opening 128 of bag 122.

The leading edge of bag 122 is then movingly gripped between cooperatingpads 66 of the second set of belts 46 and 48 along a strip below thefold line 130, but contiguous with four ply of material comprising thefolded over portion 132 of the bag; and the part of the bag above belts46 and 48 received into housing 86 through 92. At this point discreetlength of film along fold line 130 are protectively encased in hollowcentral region 82 of shields 78. Heat is applied continuously to themoving bag along fold line 130 by radiant heat from resistance heatingrods 88 and 90, but does not penetrate as severely into the areas offilm protected by moving shields 78. As may be noted, even though theshields are moving, each shield 78 continuously protects a specific areaof film as they automatically move at the same speed as bags 122.

Upon emerging from housing 86, the top end 126 of bag 122 is guidedbetween sections 118 and 120 for entrance between belts 106 and 108where the heat plastified film layers along fold line 1.30 are cooledand squeezed together simultaneously. The layers of film along the foldline are thus welded together across the width of bag 122, therebysecuring product 124 therewithin. Each shielded region, however, forms avent providing a weakened area in the weld rupturable by internalpressures; or an interrupted area in the weld sufficiently tight toretain even finely divided products, but which vents the bag for passageof excess air pressure to the surrounding atmosphere, as explained inthe aforenoted US. Pat. No. 3,439,869.

Referring now to some of the specifics of the present invention,sufficient heat can be applied to transform the film into asubstantially molten, highly heat plastified condition along fold line130. Shields 78, however, formed of metal or a like heat conductivematerial, not only serve as a shield but also readily conducts heat awayfrom the shielded area to provide a maximum cooling effect, and withoutrequiring sophisticated or expensive cooling means. Thus, even thoughthe four layers welded together might comprise heavy duty film, such as2 to l0 mil thick film, sufficient heat can be applied to form a secureweld, and yet a quality vent can be provided conveniently and in amanner acceptable for commercial usage. Moreover, the invention asillustrated can accommodate a chain of continuous bag elements eitherfilled or unfilled. Further, it is readily apparent that the method ofthe present invention can be practiced during the fabrication of bagssuch as from continuous lengths of plastic web material.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in the art that various changes and modifications can be madetherein without departing from the spirit and scope of the invention.

What is claimed is:

1. In a method of venting heat scalable plastic bag material whilesimultaneously closing the same, the material being generally of a typehaving opposed walls defining therebetween an opening, said methodcomprising the steps of:

a. folding said walls over said opening while moving said materialforward, defining a fold line extending generally in the direction ofmovement of said material;

. moving said material past radiant heating means to radiantly heatplastify the material along a select region thereof extending along saidfold line.

c. providing a plurality of heat shielding means movingsimultaneously'with said material shielding at least partially from saidradiantly applied heat, a plurality of discrete increments of materialalong said fold line as said material is moving past said radiantheating means, said shielding providing a plurality of weakened sealsalong said discrete increments of material, said weakened seals beingsufficient to form vent means in said seal upon the formation ofinternal pressures, pressing said heated layers together to form acontinuous seal along said fold line thereby sealing closed saidopening.

2. The method of claim 1 wherein said material comprises a preformedbag, said method including the step before step (a) of filling said bagwith product through said opening.

1. In a method of venting heat sealable plastic bag material whilesimultaneously closing the same, the material being generally of a typehaving opposed walls defining therebetween an opening, said methodcomprising the steps of: a. folding said walls over said opening whilemoving said material forward, defining a fold line extending generallyin the direction of movement of said material; b. moving said materialpast radiant heating means to radiantly heat plastify the material alonga select region thereof extending along said fold line. c. providing aplurality of heat shielding means moving simultaneously with saidmaterial shielding at least partially from said radiantly applied heat,a plurality of discrete increments of material along said fold line assaid material is moving past said radiant heating means, said shieldingproviding a plurality of weakened seals along said discrete incrementsof material, said weakened seals being sufficient to form vent means insaid seal upon the formation of internal pressures, pressing said heatedlayers together to form a continuous seal along said fold line therebysealing closed said opening.
 1. In a method of venting heat sealableplastic bag material while simultaneously closing the same, the materialbeing generally of a type having opposed walls defining therebetween anopening, said method comprising the steps of: a. folding said walls oversaid opening while moving said material forward, defining a fold lineextending generally in the direction of movement of said material; b.moving said material past radiant heating means to radiantly heatplastify the material along a select region thereof extending along saidfold line. c. providing a plurality of heat shielding means movingsimultaneously with said material shielding at least partially from saidradiantly applied heat, a plurality of discrete increments of materialalong said fold line as said material is moving past said radiantheating means, said shielding providing a plurality of weakened sealsalong said discrete increments of material, said weakened seals beingsufficient to form vent means in said seal upon the formation ofinternal pressures, pressing said heated layers together to form acontinuous seal along said fold line thereby sealing closed saidopening.